A pressure reducer is disclosed in U.S. Pat. No. 3,811,465. In the pressure reducer disclosed in this patent, the valve is opened by means of a regulating element in the form of an adjustable spring and a displacing arrangement configured as a plunge coil. The regulating element is resiliently biased and preset to a base tension and the valve is opened until an equilibrium is established between the preset outlet pressure which acts on the membrane in the outlet chamber and the counterforce applied to the membrane by the adjustable spring and the plunge coil. The output pressure is continuously monitored by the regulating unit and held to the desired value by means of a control signal applied with the plunge coil. When the force of the output pressure on the membrane is in equilibrium to the oppositely directed force of the adjusting spring and the plunge coil, the regulating path is then, too, in equilibrium so that the valve remains in its center equilibrium position. The plunge-coil drive is only then without current when the biasing force of the regulating element is in equilibrium with the force on the membrane developed by the outlet pressure. That is, only for a single desired value.
It is a disadvantage of the above pressure reducer that a change of the desired outlet pressure is not possible by means of only an adjustment of the regulating element. A change in the biasing force of the regulating element would be compensated by the regulating unit and has no influence on the output pressure. Furthermore, the regulating element is provided only for adjusting purposes and has only a limited adjusting possibility. In addition, a correspondence of the two adjusted values can only be obtained with difficulty by a simultaneous manual adjustment of the regulating element as well as also of the desired-value input of the control unit. However, the deviations lead to a compensation by means of the regulating unit and a loading of the plunge-coil drive. Desired value changes therefore can only occur electrically in that the plunge coil is supplied with a continuous current such that a new equilibrium adjusts itself in correspondence to the changed desired value. The range of desired values adjustable in this manner is limited by the maximum force of the plunge-coil drive.
The pressure reducer described above can therefore only be utilized in a narrow range of desired values when one does not desire to utilize an unnecessarily large drive consuming unnecessary energy.
It should be noted that even when the desired value remains unchanged, further forces act upon the above-described equilibrium on the membrane when, for example, different strokes adjust to correspondingly different through-flows. Different spring forces then occur in correspondence to the spring characteristic. Different in-flow pressures which act from within the inlet chamber on the valve also lead to similar disturbing forces which can only be compensated for by means of the plunge-coil drive in the known pressure reducer.